Various types of optical systems that utilize different operational principles exist. For instance, an afocal lens has no focusing power and transfers parallel light rays of one beam diameter to parallel light rays of another diameter. By adding a single focusing lens after the afocal system, a parfocal lens is created. In a conventional zoom lens system, only the lens elements of the afocal portion have to be moved forth and back to obtain the zoom effect, while the focusing lens can remain static. Consequently, a parfocal lens stays in focus when magnification/focal lengths are changed.
In another approach, a varifocal lens system is sometimes used in today's optical systems. The varifocal system is not based on the transfer of parallel light rays of one beam diameter to the other. Rather, a first axially movable lens focuses or diverts the light rays towards a second (or third) lens, which is a focusing lens. In order to always obtain a sharp image in the image plane, the focusing lens cannot be static and has to be axially movable or be focus tunable. Thus, a varifocal lens adjusts the position or shape of the final focusing lens when magnification/focal length is changed.
Using either approach, conventional zoom lenses are space consuming, expensive and prone to material wear as several optical elements have to be axially shifted relative to the others by means of motorized translation stages. The potential for miniaturization of such lenses for use in cell phones, medical endoscopes, or other devices where space is at a premium is limited due to their functional principles and operation.
Attempts to overcome the above-mentioned deficiencies have been made in previous systems where focus adjustable lenses were used instead of axially shiftable fixed, non-deformable lenses. In these previous systems, the shape of the lens was changed in order to alter the focal length and other optical properties of the lens.
Unfortunately, these previous approaches still suffered from several disadvantages. More specifically, their potential to sufficiently reduce axial length while providing a high zoom factor and sufficient image size on the image sensor was still limited either due to the chosen zoom principle (e.g., afocal/parfocal systems) or due to the composition or operating principles of the deformable lenses that did not offer sufficient tuning range (e.g., electrowetting lenses or liquid crystal lenses). Consequently, the disadvantages present in these previous systems limited their application and created user dissatisfaction with these previous approaches.
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